1. Field of the Invention
The present invention relates to an apparatus and method for transmitting/receiving a reference signal in a communication system.
2. Description of the Related Art
A DownLink (DL) frame includes a MAP message area and a data area in a communication system. The data area has data bursts and pilot tones. Each data burst is a set of data tones. The MAP message area includes MAP messages, each carrying data burst allocation information indicating the positions of the data bursts in the data area.
Accordingly, MAP message decoding should precede data burst decoding data from a DL frame at a receiver. Thus, MAP messages should be transmitted with high reliability.
To increase the transmission reliability of the MAP messages, the MAP messages are generated at a low coding rate. Each MAP message may include data burst allocation information for a plurality of individual users. However, this scheme requires a large MAP message area in the DL frame, thus reducing the data area.
To address the above problem, the MAP message area is divided into a plurality of MAP message areas and data burst allocation information carried in the MAP message areas are transmitted at different transmit power levels. Each divided MAP message area includes data burst allocation information for at least one user and the transmit power levels of the data burst allocation information can be determined, taking into account the channel environments and locations of the users.
When different transmit powers are allocated to the divided MAP message areas, different transmit powers can also be applied to data areas associated with the MAP message areas. Notably, a divided MAP message area and its associated data area have different transmit power levels.
As a consequence, a ‘Power Unbalance’ occurs since a plurality of data areas have different transmit powers.
The power unbalance leads to transmission of pilot tones included in the data areas at different power levels. When the pilot tones of the DL frame have the substantially same transmit power, the receiver can carry out channel estimation using the pilot tones. However, the use of different transmit powers for the pilot tones due to the power unbalance makes pilot tone-based channel estimation difficult.
Accordingly, there exists a need for a method for performing channel estimation accurately using pilot tones, in spite of power unbalance between the data bursts of different data areas or the data bursts of different subframes.